This invention relates to multi-purpose, photographic film cassettes and more particularly, it concerns an improved apparatus for facilitating positive engagement between an advancing film strip and a film actuated pull-strip for releasing processing fluid from an initially sealed reservoir forming part of a film processing organization of such a cassette.
Multi-purpose, photographic film cassettes have been developed for use in motion picture photographic systems illustrated and described, for example, in U.S. Pat. No. 3,615,127 issued to Edwin H. Land on Oct. 26, 1971; U.S. Pat. No. 3,623,417 issued to Vito K. Eloranta on Nov. 30, 1971; and in U.S. Pat. No. 3,785,725 issued to J. F. Batter et al on Jan. 15, 1974, all of which are owned by the assignee of the present invention. In such systems, a strip of photographic film contained in a cassette can be exposed in a camera adapted to receive the cassette and then processed to provide viewable images by placing the cassette in a viewing apparatus equipped to activate a cassette contained processor upon rewinding the exposed film strip. After processing in this manner, the viewing apparatus is operated as a projector to advance the film incrementally frame by frame past the light source so that the scene to which the film was exposed is reproduced in a manner well known in the motion picture art.
In motion picture systems of the type described above, the processing operation after film exposure and before viewing entails the deposition of a uniform coating of processing fluid along the length of the film strip to effect a diffusion transfer of a negative image in a light-sensitive emulsion layer on the film strip to a positive image-receiving layer or interface. The processing fluid supply is contained in an initially closed reservoir or pod housed within the film cassette, the reservoir having a removable tear-tab closure capable of being opened upon activation of the film processor by the viewing apparatus to allow the fluid to escape from the pod and pass through a nozzle-like opening against the exposed emulsion layer of the film strip. Although the processor is operated only once in any single cassette, which following processing provides a permanent housing for the processed film strip therein, its operation to achieve a uniform and complete layer of processing fluid over the exposed emulsion layer on the film strip is vital to satisfactory operation of the overall system.
To insure retention of the processing fluid in the cassette contained reservoir or pod up to the time it is needed for the processing operation, and also in some measure to insure complete availability of the processing fluid upon initial activation of the processor, the processing fluid reservoir in such systems is provided with a relatively large opening covered initially by a releasably bonded tear-tab closure capable of being completely peeled from the opening to release the processing fluid for distribution against the emulsion layer of the exposed film strip. In more advanced systems similar to the type mentioned above, the release of processing fluid from the reservoir is brought about by a pull-strip extension connected at one end to a folded back portion of the reservoir sealing tear-tab and having at its free end, a configuration adapted to engage an aperture formed in the leader end of the film strip attached to the supply spool during initial rewind rotation of the supply spool. The pull-strip, which may be mylar or other similar material is initially supported and constrained to an essentially Z-shaped path in which the intermediate leg is established by a channel formed by internal cassette walls. At its exit from the channel, the extension is bent back on itself without exceeding the elastic limits of the material from which it is made so that the projecting free end lies yieldably against the outer convolutions of the film strip on the supply spool. As the film strip pays out from the supply spool during exposure, the free end of the pull-strip will move inwardly due to the diminishing diameter of film strip convolutions on the supply spool until the film strip is completely exposed. At this time, an aperture in the supply spool connected leader end of the film strip will have passed the free end of the pull-strip extension so that upon rewinding of the film strip back onto the supply spool the free end of the pull-strip will engage the film strip aperture and become entrained between successive convolutions of the film strip supply spool leader. Continued rewind rotation of the supply spool effects a pulling action on the pull-strip and correspondingly, a peeling of the tear-tab closure from the processing fluid reservoir to release the processing fluid for application thereof to the exposed film strip.
Such an arrangement for release of processing fluid from the reservoir is shown and described in U.S. Pat. No. 3,895,862 issued to Joseph A. Stella et al. on July 22, 1975. As described in detail in this patent, the pull-strip is provided with a tapered necked down latching tongue configured to engage a bottle-shaped aperture in the film strip defined by an elongated engaging section and a locking section communicating with the engaging section through a necked down passageway. Following complete payout of the film strip from the supply reel and upon initial rewind movement of the film strip back onto the supply reel, the latching tongue engages the elongated section of the bottle-shaped aperture and upon further rewinding of the film strip the latching tongue engages the film reel hub and as the film strip continues to be rewound upon the reel, the pull-strip is placed in tension as the resisting force of the tear-tab is encountered by the advancing film strip/pull-strip combination. The necked down portion of the latching tongue is intended to pass through the necked down portion of the bottle-shaped aperture in the film strip and into positive engagement with the locking portion of the aperture in response to this resisting force. Such a locking engagement between the tear-tab actuating pull-strip and the film strip is extremely important as it is desirable for the pull-strip to remain positively attached to the film strip during subsequent projecting of the processed film strip in order to preclude problems which would be encountered were the pull-strip to separate from the film strip and possibly interfere with operation of the cassette. In some applications the frictional forces between the bent over latching tongue and the hub-surface and the interleaved film strip and pull-strip have been in excess of the force required to remove the tear-strip from the processing fluid reservoir and accordingly sufficient force has not always been available at the interface of the necked down portion of the latching tongue and the necked down portion of the film strip aperture to pull the latching tongue into locking engagement with the locking portion of the aperture.